The purpose of this research is to better understand people's ability to manage more than one task at the same time, ands, in particular how that ability changes with advancing age. Specifically, the research will examine sources of difficulty in executing two overlapping tasks and in switching between tasks as the situation requires. In addition to behavioral studies, techniques for neuroimaging will be used to explore the areas of the brain that are activated by such high level cognitive demands, and how that activity is altered by structural or functional changes in the aging brain. The ability to manage multiple tasks is a regular and often vital part of everyday life and may well be impaired in old age. Examples range from simply preparing dinner (using a variety of potentially dangerous implements) to tending to a needy child or invalid while carrying out the tasks of daily living, to operating a vehicle (which may range from a passenger automobile to a jumbo jet).